FR2512002A1 - PROCESS AND PLANT FOR THE MANUFACTURE OF SODIUM MONOHYDRATE CARBONATE - Google Patents

Abstract

1. Process for manufacturing sodium carbonate monohydrate, according to which anhydrous sodium carbonate and water are mixed with an aqueous suspension of sodium carbonate monohydrate crystals at a temperature below the transition point of sodium carbonate monohydrate to anhydrous sodium carbonate, the resulting mixture is homogenised and the crystals of sodium carbonate monohydrate are separated, characterised in that, to mix the anhydrous sodium carbonate with the suspension, the anhydrous sodium carbonate is introduced in a suspension zone in which a vortex is created.

Description

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  Process and installation for the production of sodium carbonate monohydrate SOLVAY & Cie (Société Anonyme The present invention relates to a process for the production of sodium carbonate monohydrate from carbonate

anhydrous sodium.

  The manufacture of sodium carbonate monohydrate from anhydrous sodium carbonate is commonly used to obtain dense anhydrous sodium carbonate (commonly called dense soda) from light anhydrous sodium carbonate (commonly known as light sodium hydroxide ( Te-Pang 'aou, 1969, Manufacture of Soda,

  second edition, Hafner Publishing Company, New York).

  It is generally important for industry, and in particular in glass and steel, to have dense anhydrous sodium carbonate, well crystallized, free of fines and having a

good abrasion resistance.

  When dense anhydrous sodium carbonate is obtained by dehydration of sodium carbonate monohydrate crystals, its crystalline morphology and its properties, in particular its apparent specific weight, depend on the crystalline morphology

  sodium carbonate monohydrate.

  To this end, in Belgian patent BE-A-661,071 (Allied Chemical Corporation), a method is proposed for crystallizing sodium carbonate monohydrate from anhydrous sodium carbonate, and in particular light anhydrous sodium carbonate, according to which anhydrous sodium carbonate and water are added to an aqueous suspension of crystals of sodium carbonate monohydrate in a crystallizer at a temperature below the transition point of sodium carbonate monohydrate to anhydrous sodium carbonate, the resulting mixture is subjected to a strong turbulence to make it homogeneous, part of the resulting homogeneous mixture is drawn off, which is divided into a first fraction containing only fine crystals and a second fraction containing mainly large crystals of sodium carbonate monohydrate, the crystals of the second fraction and we recycle the first fraction

in the crystallizer.

  In this known process, obtaining a homogeneous dispersion of anhydrous sodium carbonate in the mixture has generally proved to be a difficult operation, the grains of anhydrous sodium carbonate having a tendency to float and agglutinate on the surface of the bath. To avoid this drawback and to ensure sufficient dispersion of the anhydrous sodium carbonate in the mixture, it is generally necessary to subject the latter to very intense and long-lasting turbulence. This however has the disadvantage of increasing the cost of production of the carbonate. sodium monohydrate and reduce the productivity of the process The turbulence further leads

  to the additional disadvantage of causing significant breakage of -

  crystals of sodium carbonate monohydrate and to give rise to a significant production of fine crystals, so that the process requires a subsequent classification of the crystals of sodium carbonate monohydrate withdrawn from the crystallizer and recycling

fine crystals.

  The invention aims to remedy these disadvantages of the known process described above, by providing a process which makes it possible to obtain directly, and more economically, regular crystals of sodium carbonate monohydrate from anhydrous sodium carbonate and which does not no longer requires a subsequent classification of the crystals, these being suitable, as such, for obtaining

  good quality dense anhydrous sodium carbonate.

  The invention therefore relates to a process for the manufacture of sodium carbonate monohydrate, in which anhydrous sodium carbonate and water are mixed with an aqueous suspension of crystals of sodium carbonate monohydrate, at a temperature below the transition point. sodium carbonate monohydrate to anhydrous sodium carbonate, the resulting mixture is homogenized and the crystals of sodium carbonate monohydrate are separated; according to the invention, to mix the anhydrous sodium carbonate with the suspension,

  introduces anhydrous sodium carbonate into an area of the suspension

  sion, in which a vortex is generated.

  In the implementation of the process according to the invention, the origin of the anhydrous sodium carbonate is not critical. Advantageously, crystals of light anhydrous sodium carbonate are used, resulting from the calcination of sodium bicarbonate obtained by

proceeded with ammonia.

  In general, the amount of water to be used must be approximately equal to the amount of water required to hydrate the anhydrous sodium carbonate to sodium carbonate monohydrate. It is possible to deviate from the amount strictly necessary to hydration of sodium carbonate, if

  1 Q we accept a dilution or partial concentration of the above

  board of sodium carbonate monohydrate crystals.

  According to an advantageous embodiment of the method according to the invention, at least part of the water is used in the form of a saturated aqueous solution of sodium carbonate; it is advantageous to use for this purpose the mother liquor collected after separation of the sodium carbonate monohydrate crystals from

suspension.

  The initial suspension of sodium carbonate monohydrate crystals can be carried out in various ways and is not critical. It can, for example, come from a source external to the process or be obtained by partial evaporation of a solution.

aqueous sodium carbonate.

  In general, the concentration of the aqueous suspension of sodium carbonate monohydrate is advantageously adjusted so that it contains between 20 and 60%, preferably between 30 and 55%, by weight.

  crystals of sodium carbonate monohydrate.

  It has been found to be especially advantageous to use an aqueous suspension of sodium carbonate crystals monohydrate containing dissolved sodium chloride. It has in fact been observed that, all other things remaining equal, the presence of chloride

  of sodium dissolved in the suspension ensures better crystal-

  lization of sodium carbonate monohydrate-during the process and

  inhibits the formation of incrustations on the walls of the crystallizers.

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  -4 - As a general rule, good results are obtained with a sodium chloride content by weight of between 3 and 17%, preferably

  between 8 and 12%, of the weight of the suspension.

  Sodium chloride can be introduced into the suspension of crystals of sodium carbonate monohydrate in the solid state or

by any other means known per se.

  The temperature of the suspension of sodium carbonate mono-

  hydrated during the execution of the process according to the invention must be chosen low enough that the anhydrous sodium carbonate

  introduced into the suspension crystallizes therein in the monohydrate state.

  The choice of the optimum temperature depends on various factors, in particular the concentration of the suspension of crystals of sodium carbonate monohydrate and the granulometry of the crystals, as well as the granulometry and morphology of anhydrous sodium carbonate It can be determined in each particular case

  through routine laboratory work.

  As a general rule, a temperature is chosen such that its deviation from its transition point is between approximately 2 and approximately 250 ° C., preferably less than 15 ° C., the best results being generally obtained with a deviation understood

between 3 and 10 'C.

  Anhydrous sodium carbonate mixed with the suspension can

be at room temperature.

  However, it is preferred, according to an advantageous embodiment of the method according to the invention, to use hot anhydrous sodium carbonate, preferably being at a temperature

  at least equal to the temperature of the suspension.

  All other things remaining equal, the sodium carbonate monohydrate crystals obtained in accordance with this embodiment of the invention have a particle size distribution which is characterized by a larger average diameter of the crystals and by a higher homogeneity index, the homogeneity index being, by definition, the slope of the line representing the cumulative particle size distribution in a logarithmic diagram by Rosin Rammler (G Herdan, Small particle statistics, second edition,

  1960, Butterworths editors, Great Britain, pages 86 to 88 and 99 to 101).

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  In general, in this particular embodiment of the process according to the invention, good results are obtained by using anhydrous sodium carbonate being at a temperature between 90 and 2000 ° C., preferably between 100 and 1500 C. The temperature of the water mixed with the suspension of sodium carbonate monohydrate is not critical. In general, it can be adjusted as a function of the other parameters of the process, to achieve the desired temperature in the suspension. of

sodium carbonate monohydrate.

  In the process according to the invention, the anhydrous sodium carbonate is introduced into an area of the suspension of carbonate of

  sodium monohydrate, where a vortex is generated.

  The term vortex is intended to denote a vortex flow as defined in the kinematic theory of fluids, characterized by circular and concentric current lines for which the speed at each point has a normal component zero and a circumferential component inversely proportional to the radius of the current line (International Encyclopedia of Science and Technology, Vol 10, 1973, Larousse,

  Presses de la Cité, pages 535 to 537).

  In the process according to the invention, the function of the vortex is to transfer the anhydrous sodium carbonate within the suspension of sodium carbonate monohydrate downstream of the vortex It is usually a descending vortex, for example a vertical vortex

descending.

  The intrinsic characteristics of the vortex (circumferential speeds

  (depth, diameter) depend on various factors, in particular the dimensions of the crystallizer, the particle size of the anhydrous sodium carbonate, its temperature and its feed rate, the concentration of the suspension of sodium carbonate monohydrate, its viscosity and its temperature - They must be determined in each particular case by work

routine in the laboratory.

  The flow of the suspension, downstream of the vortex, must be

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  -6- set to allow the transfer, inside of it, of

  particles of anhydrous sodium carbonate entrained with the vortex.

  In the context of the invention, flows which are very suitable, downstream of the vortex, are those comprising a rectilinear translation in the extension and the direction of the vortex, for example a vertical downward translation in the case where the

  creates a vertical descending vortex.

  According to a particularly advantageous embodiment of the method according to the invention, a straight translation without rotation is implemented downstream of the vortex. This embodiment of the method according to the invention has the advantage of ensuring excellent penetration grains of anhydrous sodium carbonate from the vortex in the suspension of sodium carbonate monohydrate It also avoids excessive turbulence of the suspension and it leads to the production of well-formed crystals of sodium carbonate monohydrate, the particle size distribution of which is characterized by an average grain diameter and a homogeneity index which are well suited for the subsequent manufacture of dense anhydrous sodium carbonate, of apparent specific gravity at least equal to

  0.9 kg / dm 3 and generally greater than 1 kg / dm 3.

  To accelerate the penetration of the grains of anhydrous sodium carbonate into the suspension downstream of the vortex and to further improve the quality of the crystals of sodium carbonate monohydrate, it has proved to be especially advantageous, according to a particular embodiment of the process according to the invention. invention, to generate, around the vortex, an annular current of the suspension of sodium carbonate monohydrate and to subject this current to a translation

  straight in the same direction as the vortex, without rotation.

  To ensure efficient crystallization of sodium carbonate monohydrate, while limiting the size of the crystallizer used, it is possible, according to a preferred embodiment of the method according to the invention, to subject the suspension to a continuous flow comprising the vortex and optionally the above-mentioned parallel annular flow, a rectilinear translation, preferably without rotation, downstream of the vortex, in the same direction as the latter and a

  straight translation in opposite direction, without rotation.

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  In the implementation of the method according to the invention, it is possible to

  work either continuously or disconnected

  continuous. The invention also relates to an installation for implementing the method according to the invention, comprising, on the one hand, a crystallization chamber in communication with an anhydrous sodium carbonate intake device, with an intake device of water and with a device for withdrawing an aqueous suspension of crystals of sodium carbonate monohydrate and, on the other hand, a device for separating the crystals of sodium carbonate monohydrate from the aqueous suspension withdrawn from the crystallization chamber; according to the invention, the crystallization chamber comprises: a vertical cylinder enclosure, a vertical column open at its upper and lower ends and arranged in the enclosure, below the normal level of the suspension of crystals of sodium carbonate monohydrate, a chimney vertical, open at its upper and lower ends and arranged in the upper part of the column, a means for generating a rectilinear vortex descending in an aqueous suspension of crystals of sodium carbonate monohydrate in the chimney, means for subjecting an aqueous suspension of sodium carbonate monohydrate contained in the column in a downward vertical translation; and the anhydrous sodium carbonate intake device comprises

  a duct which opens into the chimney.

  In the installation according to the invention, the means for generating the vortex can for example consist of a propeller housed in the

  bottom of the chimney and coupled to a vertical tree.

  Any known means can be used to generate a vertical translation of the suspension of sodium carbonate monohydrate in the column, for example a gas siphon device, a turbine or

a helix.

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  -8 - In a particular embodiment of the installation

  according to the invention, vertical deflectors are fixed transversely

  Lement to the wall of the column, inside thereof and vertical partitions are arranged radially in the annular chamber formed between the wall of the enclosure and the column. In this embodiment of the invention, the deflectors and the partitions have the function of opposing a rotation of the suspension of sodium carbonate crystals monohydrate during its vertical downward translation in the column and its translation

  vertical upward in the annular chamber around the column.

  In an advantageous embodiment of the installation according to the invention, the chimney is arranged axially in the column and the means for generating the vortex and causing the suspension in the column consist of a propeller placed in the column, under the chimney, and coupled to a vertical tree

of rotation.

  This embodiment of the installation according to the invention has the advantage of being simpler in construction and of ensuring symmetrical circulation of the suspension of sodium carbonate.

  monohydrate in the crystallization chamber.

  Special features and details of the invention will emerge from

  the following description of some embodiments of the invention

  tion with reference to the accompanying drawings.

  Figure 1 of the drawings is a diagram of an installation

  implementing the method according to the invention.

  Figure 2 shows schematically in axial vertical section, a first embodiment of the crystallization chamber of

  the installation according to the invention shown diagrammatically in FIG. 1.

  Figures 3 and 4 are horizontal cross sections

  respectively according to plans III-III and IV-IV of Figure 2.

  Figure 5 is a view similar to Figure 2, of a second

  embodiment of the crystallization chamber of the installation

lation according to the invention.

  In these figures, the same reference notations designate

identical elements.

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  9 9- The installation shown diagrammatically in FIG. 1 comprises a chamber 1 for the crystallization of sodium carbonate monohydrate, a silo 2 for storing anhydrous sodium carbonate, for example light sodium carbonate, a tank 3 for storing '' an aqueous solution of sodium chloride and sodium carbonate and a wringing device 4 to separate the crystals of sodium carbonate monohydrate from the drawn-off suspension

from bedroom 1.

  Conduits 5, 6 and 7 connect the crystallization chamber 1

  respectively at silo 2, tank 3 and wringing device 4.

  A conduit 8 and a pump 9 are used to recycle in the reservoir 3 the mother water collected from the wringing device 4, after separation of the sodium carbonate monchydrate crystals that the gold collects through a conduit 10 A conduit 11 is used for the water intake

tank 3.

  An oven 11 can optionally be interposed in the duct, if it is desired to preheat the anhydrous sodium carbonate before

  its admission into the crystallization chamber 1.

  FIGS. 2 to 4 show an embodiment

  particular, in accordance with the invention, of the crystallization chamber

  tion 1 of the installation of figure 1.

  In accordance with the embodiment shown in FIGS. 2 to 4, the crystallization column 1 comprises a vertical cylindrical enclosure 12, a frustoconical bottom 13, a vertical cylindrical column 14 disposed axially in the enclosure 12 and open at its upper ends and lower, and a propeller 15 placed in the lower zone of the column 14 and coupled to a shaft

vertical rotation 16.

  Two groups of vertical deflectors, respectively 17 and 18, are fixed transversely to the wall of the column 14, inside the latter; the deflectors 17, three in number, are arranged above the propeller 15 and the deflectors 18, at the

  number three, are available under the propeller 15.

  Three vertical partitions 19 are arranged radially in the annular chamber 20 formed between the wall of the enclosure 12 and

column 14.

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  - In the upper part of the column 14, a vertical cylindrical chimney 21 is arranged in the upper zone of the column 14, between the shaft 16 of the propeller 15 and the wall of the column 14 The inlet duct 5 of anhydrous sodium carbonate in the chamber 1 opens above the chimney 21. The column 14 and the chimney 21 are both placed below the normal level 22 of the bath in the enclosure 12, during

  normal operation of the installation.

  In the chimney 21 is arranged a propeller 23 coupled to a

1 o vertical rotation shaft 24.

  The enclosure 12 is also surrounded by an envelope 25 for the circulation of water or another refrigerant, to maintain the temperature in the crystallization chamber 1 to a

  substantially constant, predetermined temperature.

  During the steady state operation of the installation shown in FIGS. 1 to 4, the enclosure 12 is filled, substantially up to level 22, with an aqueous suspension of sodium carbonate monohydrate crystals in an aqueous solution of carbonate and sodium chloride and its temperature is permanently maintained a few degrees below the transition temperature of carbonate

  sodium monohydrate to sodium carbonate azide.

  Water is continuously introduced into the reservoir 3, via the conduit 11; simultaneously, anhydrous sodium carbonate and an aqueous solution of sodium carbonate and sodium chloride

  are introduced into chamber 1 via the conduits 5 and 6 respectively-

  ment and a fraction of the suspension contained in the chamber 1 is withdrawn from the latter by the conduit 7 and transferred to the wiping device 4, where crystals of sodium carbonate monohydrate, collected in 10, are separated, and a mother liquor that we recycle

  in the tank 3 via the pipe 8 of the pump 9.

  The respective flow rates of water, via line 11, of anhydrous sodium carbonate via line 5, of aqueous solution via line 6 and of suspension via line 7 are adjusted so as to avoid a variation in the level of the suspension in the crystallization chamber 1 and to maintain its crystal concentrations

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  il - sodium carbonate monohydrate and dissolved sodium chloride

substantially constant.

  For example, after having fixed the respective flow rates of anhydrous sodium carbonate via line 5 and of water via line 11, the withdrawal rate of the suspension is adjusted via line 7 to

  maintain the level 22 of the suspension in the crystal chamber-

  reading 1 substantially constant and the flow rate of recycled mother water is adjusted to maintain the density of the aqueous suspension in the

  crystallization chamber at the desired value.

  In the case where the anhydrous sodium carbonate in the silo 2 is free of sodium chloride, provision should be made for adding sodium chloride to the crystallization chamber 1; this addition of sodium chloride is easily carried out by introducing the water via the conduit 11, in the form of a brine of chloride of

sodium.

  If the anhydrous sodium carbonate in silo 2 contains sodium chloride, on the contrary, a

  mother water purge on recycling circuit 8 and additional

  of water via line 11, to compensate for the water eliminated by

the purge.

  Alternatively, instead of working continuously as described above, it is also possible to work discontinuously. For this purpose, the suspension is only withdrawn periodically from the chamber 1, via the conduit 7, and the withdrawal frequencies are adjusted so that the level of the suspension in chamber 1 varies between

  a predetermined upper limit and lower limit.

  According to the method according to the invention, the suspension contained in chamber 1 is subjected, under the action of the rotation of the propeller 15, to a continuous circulation comprising a vertical downward translation in the column 14 and an upward vertical translation in the annular chamber 20 The deflectors 17, 18 and the partitions 19 prevent rotation of the suspension in the

direction of rotation of the propeller 15.

  Simultaneously, the propeller 23 generates a descending vertical vortex

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_ 12 -

  in the part of the suspension contained in the chimney 21, the depth of the vortex being slightly greater than the height of the chimney. The particles of anhydrous sodium carbonate from line 5 fall into the chimney 21 where they are entrained by the vortex and projected into the suspension contained in the column

  12, under the chimney 21, where they are immediately dispersed.

  During the continuous circulation of the suspension in the column 12 and the annular chamber 20, the sodium carbonate

  anhydrous recrystallizes as sodium carbonate monohydrate.

  In the modified embodiment of the crystal chamber-

  1, shown in Figure 5, the propeller 23 and its shaft 24 are removed and the chimney 21 is disposed axially in the column 14 above the propeller 15 Furthermore, the duct 6 for admitting carbonate solution of sodium and sodium chloride opens into the chimney 21, above the vortex, of

  preferably near the axis of the chimney 21.

  In this embodiment of the crystallization chamber 1 of the installation according to the invention, the propeller 15 performs the dual function of generating the vortex in the chimney 21 and the translation of the suspension in the column 14 and in the annular chamber 20. To avoid the formation of incrustations on the propeller shaft, this is preferably placed entirely under the propeller and

  crosses the frustoconical bottom 13 of the enclosure 12.

  In the application examples which follow, sodium carbonate monohydrate crystals were prepared from anhydrous sodium carbonate in an installation in accordance with that shown diagrammatically.

in Figures 1 and 5.

Example 1

  An aqueous suspension containing approximately 0.45 kg of sodium carbonate was used in the crystallization chamber

  monohydrate per kg and kept there at a temperature of 95 C.

  The chimney 21 was fed with light sodium carbonate at room temperature and with an aqueous solution of sodium chloride and sodium carbonate at 60 ° C., having the following composition: Na 2 CO 3: 204 g / l 2 3 Na Cl: 104 g / l H 20: 692 g / 1 The flow rates of the light sodium carbonate and the aqueous solution were adjusted to allow continuous hourly withdrawal of 1000 kg of suspension at 45% by weight of sodium carbonate

  monohydrate, per m of the useful volume of the crystallization chamber 1.

  The test was continued uninterruptedly for 48 hours and samples of the sodium carbonate monohydrate crystals collected periodically were taken every four hours and the particle size analysis of the samples was carried out. The results are

recorded in Table I below.

Table I

  Particle size distribution of sodium carbonate Sample Duration of monohydrate on running N Refusal (% by weight) at diameter d (mm) Diameter Index

(hours) average homo-

  d = l d = 0.8 d = 0.5d-0.315 d = 0.250 d = 0.160 d = 0.100 d = 0.063 (mm)

  1 4 O O 7.5 33.8 58.2 85.4 95.5 98.4 0.27 2.7

  2 8 O 0 8.5 39.5 60.3 84.0 94.8 97.8 0.28 2.4

  3 12 O O 6.6 37.5 60.7 86.6 95.8 98.4 0.28 2.7

  4 16 O O 6.8 40.2 62.0 85.8 95.3 98.2 0.29 2.5

  20 O O 7.5 39.9 63.7 85.7 96.3 98.6 0.29 2.7

  6 24 O O 9.6 40.6 60.9 85.8 96.0 98.5 0.29 2.6

  7 28 O 0.1 6.7 37.6 60.8 86.7 95.9 98.5 0.28 2.7

  8 32 O 0.1 7.7 35.6 60.2 85.1 95.9 98.4 0.27 2.8

  9 36 O 0 6.9 36.0 55.3 83.0 95.2 98.1 0.27 2.5

  40 O O 7.0 44.4 65.6 86.4 95.4 98.2 0.30 2.4

  11 44 OO 9.4 40.5 63.2 85.7 95.7 98.6 0.27 2.5 12 48 O 0.1 10.1 42.2 61.2 81.1 94.8 98, 0 0.29 2.3

Average 0.282 2.57

_I,,

  4 s l l_ ra o o - By calcination of sodium carbonate monohydrate, dense sodium carbonate of specific gravity close to

1.13 kg / dm 3.

Example 2

  The test of Example 1 was repeated, preheating the anhydrous sodium carbonate to about 100 C, before introducing it into the

  reaction chamber 1 The test lasted 71 hours.

  The results of the particle size analyzes carried out on the sodium carbonate monohydrate samples are recorded in the

Table II below.

  9.4 TPU 92 (Unu) E 90 '0 PIOOT "O = PI 09 T 40 = ploçz" o = plçlú, O = pi 40-pls 4 o-pl T = p -Ouloiq apu; a, & yes (sainelq) ODTPUI, aalieulu T (11 (um) p vjz? Uiv Tp nr (sp Tod ue%) stake 'm alqz) Iem UOI gipapxqouom op opina ITIUU 14 Z) 3 mn Tpos op airuoqivv np; anb Tjtzgmolnuta Z uo Tinq Tj: 9 T (i tu CD C> w v- tel Cu 9 '16 i 7,, g 6

6 "86

  / "86 '86' 86 '96 S" 96 T'86 L 486 Z "96" 86 I 56 I 56 486

  "26

  Gas 94 Z 81 Z S'z O, ú 6 'Z SIZ 84 4 14 Z SI z 64 Z 9, z SI z 6, z SIZ 6, z zlú

89 C 40

LCO

8 ú, O

t, ú "o g Co LCO 9 CO Lúio

8 to 60

  Lú, O 9 úio 6 ú 4 o 8 CO 8 ú & O 9 CO ú, O euuaúom çi ú 1 zi L il z L "66 LI 66 84 66 84 66 9 '66 84 66

L 466 -

8 "66

  9 '66 8 '66 L 466 L 466 94 66 L 466 L 466 1 '66 L'68 Cú 6 Cú 6

'1 to 6

9 "to 6

9 'E 6

L'ú 6

9 'E 6

O '6

T'Z 6 Z '6 ú'fi 6

64 Z 6

Z ', ú 6,

0 "96

ú, ZL

1 "61

 & 6 L

Z 49 L

9 "LL

1 '6 L

7, bone

ú 4 LL

6 "ZL úILL C le 946 L

9 '6 L

  L&LL E 4 úq V ç 8, Lç z Iog LIE Il I L Oú 19

9, ú 9

946 409 8 "úç

Z 46

ç 4 z 9

6 "19

1 6 Z 9

8, Lç 048

  40 Z

  O'zz z 4 çz L & 61 ú, úz 84 çz il 4 il z 64 ZZ 9, Tz leiz 6 sz

L 4 LZ

* 1 1, E z 84 Lz L 481 'O' O 'O g IO LIO 6 IO 8, o 40

î 7 ', W

  il 4 O LIO O 'T ZIO 94 o ZIO o il ú 9 6' ç Oç L 17

 '6 ú

 ú çioú

  69 Z

úZ T çtg% D Il ntalqel

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  17 - After calcination of the sodium carbonate monohydrate collected, dense sodium carbonate of apparent specific gravity was obtained

substantially equal to 1.13 kg / dm 3.

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18 -

Claims (7)

R E V E N D I C A T I O N S   1 Process for the manufacture of sodium carbonate monohydrate, according to which anhydrous sodium carbonate and water are mixed with an aqueous suspension of crystals of sodium carbonate monohydrate at a temperature below the transition point of sodium carbonate monohydrate in anhydrous sodium carbonate, the resulting mixture is homogenized and the crystals of sodium carbonate monohydrate are separated, characterized in that to mix the anhydrous sodium carbonate with the suspension, anhydrous sodium carbonate is introduced into an area of the suspension, in which generates a vortex.   2 Method according to claim 1, characterized in that downstream of the vortex, which is rectilinear, descending, the suspension is subjected to a rectilinear descending translation in the extension of the vortex, without rotations 3 Method according to claim 2, characterized in that around the vortex, an annular current of suspension is generated which is subjected to a rectilinear translation in the direction of the vortex, without rotation. 4 Method according to claim 3, characterized in that the suspension is subjected to a continuous flow comprising the vortex and the annular current, the aforementioned straight downward translation downstream of the vortex and an upward straight translation without rotation.   5 Method according to any one of claims 1 to 4,   characterized in that an aqueous suspension of sodium carbonate monohydrate containing from 30 to 55% by weight of crystals of sodium carbonate monohydrate and from 8 to 12% by weight is used dissolved sodium chloride.   6 Method according to any one of claims l to 5,   characterized in that the temperature of the suspension is adjusted so that its difference with the transition point of the sodium carbonate monohydrate to anhydrous sodium carbonate is between 3 and 100 C and the anhydrous sodium carbonate is heated to a 12002   19 - temperature at least equal to the temperature of the front suspension to mix it with it.   7 Installation for the manufacture of sodium carbonate monohydrate according to the process according to any one of   Claims 4 to 6, comprising, on the one hand, a   crystallization (1) in communication with an anhydrous sodium carbonate intake device (5) with a water intake device (6) and with a device for drawing off an aqueous suspension of sodium carbonate monohydrate crystals (7) and, on the other hand, a device for separating the sodium carbonate monohydrate crystals from the aqueous suspension withdrawn from the crystallization chamber, characterized in that the crystallization chamber (1) comprises a vertical cylindrical enclosure (12 ), a vertical column (14) open at its upper and lower ends and arranged in the enclosure, below the normal level of the suspension of sodium carbonate crystals monohydrate a vertical chimney (21) open at its upper and lower ends and arranged in the upper part of the column, a means (23,15) for generating a rectilinear vortex descending in an aqueous suspension of crystals of sodium carbonate monohydrate in the chimney (21) and a means (15) for subjecting an aqueous suspension of sodium carbonate monohydrate contained in the column (14) to a vertical downward translation, and in that the device for admitting anhydrous sodium carbonate comprises a   conduit (5) which opens into the chimney (21).   8 Installation according to claim 7, characterized in that the chimney (21) is disposed axially in the column (14) which is itself 8 axially disposed in the enclosure (12) and in that the means for generating the vortex and the means for subjecting the suspension to translation in the column consist of a propeller (15) arranged in the column, under the chimney, and in that vertical deflectors (17, 18) are fixed transversely to the wall of the column ( 14), inside thereof and vertical partitions (19) are arranged radially in the annular chamber (20) formed between the wall of the enclosure (12) and the column (14). _ 20 -   9 Installation according to claim 8, characterized in that the propeller (15) is coupled to a vertical rotation shaft (16)   which is arranged entirely under the propeller (15).   Installation according to any one of claims 7   9, characterized in that the water intake device comprises a conduit (6) which opens into the chimney (21) and in that the device for extracting the aqueous suspension comprises a conduit   (7) which opens into the enclosure (12), under the column (14).